U.S. Pat. No. 4,781,495 and U.S. Pat. No. 4,929,370 disclose methods for drilling a hole in a printed wiring board material in which, when a hole for conduction between front and reverse surfaces is made with a drill, one surface or each surface of the printed wiring board material is provided with a sheet obtained by impregnating a porous sheet such as paper with a water-soluble lubricant, concretely a mixture of glycols such as diethylene glycol or dipropylene glycol, a synthetic wax such as a fatty acid ester, and a nonionic surfactant. However, these methods have defects. The defects are that the effect of preventing heat generation of a drill is insufficient, that the impregnation of the porous sheet with the above mixture is poor and that the sheet is sticky.
As means for solving the above defects, JP-A-4-92494 and JP-A-6-344297 propose drilling methods using a sheet composed of polyethylene glycol or polyether ester and a water-soluble lubricant. However, although the above methods improve the quality of a drilled hole and provide an improvement in stickiness, the winding tendency of a resin around a drill bit becomes pronounced. In some cases, there is found a decrease in hole-location accuracy due to run-out. Therefore, a further improvement is necessary. There is found a tendency that such a decrease in hole-location accuracy increases with decreasing the diameter of a drill bit. Therefore, improvements are required for applying the above methods when a drill having an extreme small diameter is used.